This proposal is designed to study the mechanisms of immunodeficiency associated with cancer and other human diseases. A particular emphasis is placed on the nature of the effector and regulatory cells as well as the role of soluble factors such as prostaglandins, interferon and other materials produced by cancer and non-neoplastic cells in the modulation of the immune response in such patients. Specifically, we intend to investigate the phenotype and other functional properties of the human natural killer (NK) cell, to investigate the mechanism of measles-virus induced suppression of T cell mitogenesis, to investigate the mechanism of impaired NK activity in some cancer patients, to determine the effect of indomethacin administered in vivo on the T cell immunodeficiency of selected cancer patients, and to determine if the immune defects (prostaglandin-producing suppressor cell or impaired NK activity) found in some cancer patients can be identified in family members.